1. Field of the Invention
The present invention relates to a method and apparatus for cleaning a wellbore with specially configured drill string mounted tools. More particularly, the present invention relates to a tool apparatus that enables debris removal tools (e.g., scraper blades, brushes or magnetic members/magnets) to be mounted to the outer cylindrically shaped surface of a section or joint of a drill string/drill pipe with a specially configured locking clamp or clamps.
2. General Background of the Invention
The Drilling of an oil well typically requires the installation into the wellbore of steel walled casing. This casing is cemented into place to provide a gas tight seal between the overlapping casing strings and also between the casing and the formation or rock through which the well is drilled. Typical cementing practice requires the cement to be pumped from the surface area or wellhead down a string of internal tubing or down the inner most casing string and displaced through the bottom of the casing string into the casing annulus. This procedure may contaminate the inside of the casing wall or wellbore with the cement. After cementation is completed, it is often required to drill out cement and the associated cementation equipment (commonly referred to as shoe track, floats shoe, landing collar, and darts).
Chemicals, solids, greases and other fluids used in the drilling process can and do adhere to the casing wall. These chemicals often mix to become a sticky and viscous substance which is largely resilient to chemical treatments and difficult to remove. As the wellbore casing is steel walled, it can and is prone to rusting and scaling.
During the drilling and other downhole activities, pieces of the drilling or wellbore equipment may need to be milled. Through various other processes (purposeful or accidental), pieces or parts can be left inside the wellbore. The aforementioned situations result in contaminants being left in the wellbore, which will for the purposes of this document be referred to as debris.
During the completion phase in a well lifecycle, several pieces of hardware are semi-permanently installed into the wellbore. These vary greatly in complexity and cost. Their primary function is the transportation of produced hydrocarbons (or injection from surface of other fluids) between the reservoir and the Christmas tree/wellhead (or vice versa) as well as maintaining hydrostatic control of the wellbore at all times. Completions typically include steel tubular piping to transport the fluids, at least one hydrostatic sealing device (packer) and one safety valve. More complex completions may include gauges to measure pressure and temperature at multiple points in the wellbore. Other items may include chokes, screens, valves and pumps. Advancements in downhole electronics make the placement of measuring and controlling equipment more accessible and more commonplace.
Typically these components are sensitive to debris. It has been well documented that debris is a leading root cause of failure during completion operations. In response, a niche industry has developed since the late 1990s, which is focused on the removal of debris and the cleaning of the wellbore. This niche of the oil industry is known as wellbore cleanup. The wellbore cleanup operations will typically take place between the drilling and completion of the well.
Generally speaking, the practice of wellbore cleanup is not new. Examples of prior art go back many years when basic embodiments of wellbore cleanup tools were developed, including scrapers, brushes, magnets, junk catchers and variations thereof. These were basic tools designed to fit a basic need, examples of which are still in use today.
As advancements in drilling and completion technologies were made (particularly starting in the 1990's with the inclusion of downhole electronics, sand control, intelligent completions and extended reach drilling) improvements to the design and functionality of wellbore cleanup tools were marketed, and the practice of improving the cleanliness of oil wells prior to installation of the completion components became almost standard practice. During the wellbore cleanup operations, an assembly of tools (referred to as a bottom hole assembly or BHA) will be run into the wellbore to clean each casing section. These tools are fastened together using threaded connections located at either end of the tool. The tools or BHA are then fastened together with the drill string or work string consisting of multiple lengths of drill pipe, collars, heavy weight drill pipe, wash pipe or tubing also featuring threaded connections. These threaded connections are typically industry standard connections as defined in ANSI/API Specification 7-2 (for example 4-½″ IF/NC50 or 3-½″ IF/NC38) and commonly referred to as API connections. Also available are proprietary connections which are licensed from manufacturers of high strength drill pipe. Popular proprietary connections are supplied by NOV-Grant Prideco (eXtreme Torque, HI Torque, Turbo Torque), Hydrill (Wedge Thread) and others. The proprietary connections are often referred to as premium drill pipe connections and are typically used when higher mechanical strengths are required (e.g., torque, tensile strength, fatigue resistance, etc.) or when larger diameter drill pipe is preferred relating to the improvement of drilling hydraulics. For example, it is common now to use 5-⅞″ OD drill pipe inside 9-⅝″ casing to improve hydraulics whereas in the past it would have been more common to use 5″ drill pipe).
The table below shows some examples of drill pipe and connection combinations used for a typical casing size; however, due to the many manufacturers and standards available, there may be thousands of combinations.
Note: The Drill Pipe OD refers to the Pipe Body OD and not the maximum external of the component. The Tool Joints are always of larger diameter. Also the Casing Size is defined by the Nominal OD and the linear weight per foot. API 5-CT allows for a tolerance in the diameter and ovality. Therefore the Casing ID may vary significantly.
Casing SizeTypical Nominal CasingODIDDrill Pipe ConnectionsDrill Pipe ODDrill Pipe Tool Joint OD9.625″8.374″-8.921″API NC50 (4-½″ IF)5.0″6.375″-6.750″9.625″8.374″-8.921″TT/HT/XT505.0″6.375″-6.750″9.625″8.374″-8.921″TT/HT/XT555.5″ 7.0″-7.375″9.625″8.374″-8.921″TT/HT/XT575.875″ 7.0″-7.375″9.625″8.374″-8.921″WT505.0″6.5/8″-7.0″  9.625″8.374″-8.921″WT545.5″7″9.625″8.374″-8.921″WT565.875″7″-7-¼″
Wellbore cleanup tools come in a variety of types and brand names. However, they can be categorized generally as one of the following: a scraper, brush, magnet, junk basket, debris filter, circulation sub, drift or a combination of two or more of these. These tools shall typically consist of a tool body onto which the various components can be attached. The tool body may consist of one or more pieces, but shall in all cases include threaded drill pipe connections, either API or Premium type. The tool body is typically an integral drill string component when made up into the drill string and shall bear all the tensile, torque, fatigue and pressure loading of the drill string. The tool body is typically made of steel and customized to allow attachment of the various components in order for it to function in the manner described.
Due to the many variations of drill pipe connections, the variety of casing sizes, and the many types of wellbore cleanup tools required, it would be commercially impractical for a company providing wellbore cleanup tools to stock every combination required from every customer. Therefore the practice of designing wellbore cleanup tools to cover a range of casing sizes as well as a variety of functions has become common practice, whereby the tool body can be used with interchangeable external components to cover both the size range and in some cases also to alter the function of the tool (for example from a scraper to a brush). This allows standardization of the tool body, however as the drill pipe connections are hard cut onto the tool body, a degree of standardization of the tool body connections are required. Typically this is the API drill pipe connection common to that casing size (NC50 for 9-⅝″ casing or NC38 for 7″ casing). In some cases the wellbore cleanup tool manufacturer may supply the tools with premium drill pipe connections, however for commercial reasons this is usually limited to specific projects or markets where the use of the corresponding drill pipe justifies this.
It is common for suppliers of wellbore cleanup tools to supply either individual tools or assemblies of tools where the individual tools have a type of drill pipe connection which is not the same as that used in the drill string. In this case it is common for the tools to be supplied with crossovers. Crossovers are typically short “subs” (joints of tubing) with differing connections at each end. For example, a XT-57 box thread can be at the top with an API NC50 pin at the bottom. This allows components of the drill string with non-interchangeable threaded end connections to be made up together into a singular integral drill string. Further to this, it is often practice to supply pup joints which are typically ten feet (10′) or less in length and have a profiled external diameter which matches the drill pipe and which fits into the drilling elevators and drill pipe slips to facilitate the installation and removal of the drill string into/from the wellbore in a timely fashion. There also exists pup-overs which are a combination of pup joint and crossover and which combines the functionality of both.
Wellbore cleanup tools and drill string often have mismatching threaded connections, and the wellbore cleanup tools are usually rated to lower strengths. The lower strength of the cleanup tools in effect reduces the overall strength of the drill string, which is typically rated by the strength of its weakest link. This has become an acceptable practice provided the drilling parameters do not exceed the limitations of the weakest point. The situation can arise during the cleanup operations that high torque can be observed during rotation of the drill string which results in rotation of the string being suspended. Drill string rotation is a key function of wellbore cleanup in the removal of debris from the wellbore, the lack of which significantly impacts the efficiency and effectiveness of the wellbore cleanup.
The requirement to include crossovers and pup joint into the drill string increases the number of threaded connections into the drill string which in turn increases the time and cost to deploy the drill string, increases the inspection costs and increases the likelihood of failure. The inventory of crossovers and pup joints needs to be managed, which includes storage, handling, inspections and maintenance. Due to the many types of drill pipe connections and the varying sizes, and the need to maintain sufficient inventory for multiple overlapping operations, the stocking and management of these inventories is a cost prohibitive endeavor.